Update mvneta/e6000sw for new DSA Device Tree Bindings

Description

Update mvneta/e6000sw for new DSA Device Tree Bindings

In the latest Linux kernel revisions the DSA (Distributed
Switch Architecture) device tree binding was changed.
Instead of the top level dsa@ node, the switch and its
ports is represented as a child node of the mdio bus.
With that other modifications were added, such as
relation with the ethernet port of the SoC. Adjust
e6000sw etherswitch and mvneta drivers to that.